The present invention relates generally to micro-inverters designed to convert DC energy from a solar panel to AC energy suitable for grid connected applications. More particularly, the present invention relates to single stage, isolated micro-inverters having controllers for alternating operating modes in an H-bridge converter topology.
Traditionally, systems utilizing solar energy have relied on centralized inverters having a plurality of solar panels providing an output into a single unit. This type of system has certain drawbacks, most notably in the costs involved but also in efficiency. For this reason solar energy has often been an energy source of the last resort where no other form is reasonably available.
More recently, “micro-inverters” have been developed to reduce the costs and increase the efficiency with which solar energy may be captured and converted. Each solar panel, or photovoltaic panel, provides a DC signal to an individual associated micro-inverter, which converts the DC signal to an isolated AC output that is suitable for many standard household operations. The various AC outputs may further be combined and suitable for grid-connected applications.
Many topologies have been investigated, published and patented in recent years. However, for these micro-inverters the most promising approach to achieve the required efficiency appears to be single-stage, current-fed isolated inverters. In these topologies the converter carries out the functions of maximum power point tracking (MPPT), current shaping, and insulation between the photovoltaic (PV) panel and the grid all at the same time.
Current transition mode is commonly used to obtain high energy conversion efficiency. This operative mode, if a traditional approach is used, leads to a very broad switching frequency operative range. This fact increases converter losses, making it very difficult to properly control the output current. Further, the broad switching frequency range makes it almost impossible to implement a DSP-based fully digital control.
Therefore, there is a need for a system and method for more efficiently converting solar-based DC energy to AC energy suitable for grid connections.
Further, there is a need for a system and method for a converter topology having an operating mode that facilitates improved control functions and reduces cost.